In the field of optical information processing, as well as in optical communication, the need for developing an optical switching technique which effects direct path switching of a large amount optical signal information, in an optical signal, without transforming the optical signal to the corresponding electrical signal, is increasing. A large variety of techniques, ranging from an assembly of a planar optical waveguide on a substrate of e.g. quartz glass, semiconductor, lithium niobate or a polymer, up to a switch of a large scale having a movable unit of an extremely small size, such as a micro-machine, has so far been devised.
The switch including a micro-machine has a movable part and hence is complex to manufacture. It also suffers the problem that it is not that easy to procure operational reliability, and that it is difficult to increase the switching speed.
Another example of the optical switch, implemented by a planar optical circuit, is a multi-input and multi-output optical switch composed of a plural number of one-input two-output units and a plural number of two-input two-output units, as basic units, arranged in a matrix configuration. Taking an example of a four-input four-output matrix optical switch, eight 1×2 switch units and four 2×2 switch units are needed. In this case, switching of optical paths in the respective switch units is by exploiting changes in the refractive index brought about by the thermo-optical effect or the electro-optical effect.
However, with this system, if the switch is increased in size and the number of channels is increased, the overall size of the device is increased, while the number of crossings of the waveguides is also increased. Consequently, there are raised a number of problems, such as increase in optical loss and in the device cost, and lowered yield.
Recently, such a system is being researched, in which the refractive index of an arrayed optical waveguide is varied to deflect the propagated light beam to perform switching of the optical path.
FIG. 4 shows a known configuration of an arrayed optical waveguide type switch (see Patent publication 1). In this known configuration, the arrayed optical waveguide type switch is formed as a planar optical circuit on a quartz substrate 71. In an arrayed optical waveguide section, the respective optical waveguides are set to equal lengths. A preset difference may be caused in the refractive indexes of the optical waveguides by applying a voltage to heater electrodes 76 differing in length from one waveguide to another.
A signal light, entered an input optical waveguide 74, is spread laterally by a first slab optical waveguide 75 so as to be distributed to the arrayed optical waveguide 77.
When the voltage, applied to the heater electrodes 76, is changed, preset changes in the refractive indexes are produced from one optical waveguide of the arrayed optical waveguide 77 to the next. The propagation direction of the light beam is deflected at input ends 79 of a second slab optical waveguide 72. This causes the light collecting point at output ends 78 of the second slab optical waveguide 72 to be changed to alter the output optical waveguide (output port) 73 for signal light.
The configuration of FIG. 4 has a merit that it is not increased excessively in size as a result of crossings of waveguides or of an increased number of channels as in the case of the above-described matrix switch. However, the configuration has a drawback that, while it allows for the one-input multiple-output function, it does not allow for the multiple-input multiple-output function.
Patent Document 2 discloses an optical switch which implements an N×N switch by interconnecting plural input ports and plural output ports by a two-dimensional light beam propagated on a slab optical waveguide. Patent Document 3 discloses an optical switch comprising a first optical deflector, a planar optical waveguide, and a second optical deflector. The first optical deflector includes a star coupler, a set of waveguide arrays and electrodes, sequentially connected to input ports, while the second optical deflector includes a star coupler, a set of waveguide arrays and electrodes, sequentially connected to output ports. The two array sets are interconnected via a planar waveguide. The waveguide light beams of an array of the first optical deflector are phase controlled by electrodes so that the light beams are caused to be incident on a desired array of the second light deflector. The waveguide light beams propagated on the array of the second optical deflector are phase controlled by electrodes to provide for the equal phase of the light beams which are then incident on the coupler. The coupler then radiates only light incident thereon in the equal phase state.    Patent Document 1: JP Patent Kokai Publication No. JP-A-11-212123 (FIG. 1)    Patent Document 2: JP Patent Kokai Publication No. JP-P2003-202606A (FIG. 9)    Patent Document 3: JP Patent Kokai Publication No. JP-A-5-273604 (FIG. 1)